Strain Wave Gear Assembly With Roller-Cam Load Alignment
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Solution Overview
Problem
Conventional strain wave drives for rotary actuation of flight control surfaces in aircraft are bulky and heavy due to the need for multiple intermeshing gears, and the added compliance to ensure correct load distribution increases costs and complexity.
Innovation Solution
A strain wave drive design featuring an elliptical wave generator shaft with a curved cam surface and roller bearings, allowing self-alignment and uniform stress distribution, reducing the need for specialized bearings and additional compliance components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional involute gears are used to provide high torque ratio, then the required torque ratio is achieved, but the size and weight of the actuator system increases
Solution Approach 1:
The patent replaces the conventional involute gear system with a strain wave gear mechanism that uses elastic deformation of a flex spline instead of rigid toothed wheels. This substitution achieves the same torque multiplication function with significantly reduced weight and size, as the flex spline's elastic compliance allows for compact design without requiring multiple heavy gear stages
Solution Approach 2:
The patent employs a flexible toothed ring (flex spline) as the core component that deforms elastically under the wave generator's action. This flexible element replaces rigid conventional gears, enabling high gear ratios in a compact package while reducing overall system weight, directly addressing the contradiction between power transmission capability and weight
2Reliability
If built-in compliance is added to ensure correct load distribution, then tooth engagement is improved, but costs and complexity increase
Solution Approach 1:
The flex spline's inherent elastic flexibility provides the necessary compliance for proper tooth engagement and load distribution. This built-in elastic compliance eliminates the need for additional compliance mechanisms or complex bearing arrangements, achieving reliable tooth contact while maintaining simple system architecture
Solution Approach 2:
The patent modifies the physical state of the flex spline to be elastically compliant rather than rigid, allowing it to deform and conform to the wave generator's elliptical motion. This parameter change (from rigid to elastic) inherently provides the compliance needed for correct load distribution without adding complex compliance components
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves a compact, lightweight strain wave drive with reduced manufacturing and assembly complexity, maintaining performance while minimizing size and weight, and ensuring uniform load distribution across the gear teeth.
Implementation Method 1
roller bearings provided between the cam surface and the flex spline
Data Source
Figure 1A~1B
Figure 2~4
Figure 3
AI summary
A strain wave drive comprising: an elliptical wave generator shaft (100) rotatable about an axis (X); a flexible flex spline (500) mounted around the wave generator shaft; a ring gear assembly mounted around the flex spline, the ring gear assembly comprising an output ring gear (200) having a circular inner periphery and being sandwiched between two earth ring gears (300, 400) each having a circular inner periphery; wherein the flex spline has a first number of radially outwardly extending teeth around its outer periphery; and wherein each earth ring gear has the first number of radially inwardly extending teeth to engage with the teeth of the flex spline; and wherein the output ring gear has a second number of radially inwardly extending teeth, such that as the wave generator shaft rotates, it causes the flex spline to take up the elliptical form of the wave generator shaft and the teeth of the flex spline engage with teeth of the output ring gear at the major diameter of the ellipse, causing the output ring gear to rotate; and wherein the wave generator shaft is provided with a radially outer cam surface defining the elliptical shape and arranged to engage with an inner surface of the flex spline; the strain wave drive further comprising roller bearings provided between the cam surface and the flex spline, and wherein the cam surface is a curved surface.